Optical-fiber ribbon with spaced optical-fiber units

ABSTRACT

An optical-fiber ribbon includes optical fibers (e.g., reduced-diameter optical fibers) arranged in parallel within optical-fiber units, wherein at least one adjacent pair of optical-fiber units is separated by a longitudinal adhesive-free spacing for a portion of the optical-fiber ribbon&#39;s length. Typically, each adjacent pair of optical-fiber units is separated by an adhesive-free spacing for a respective portion of the optical-fiber assembly&#39;s longitudinal length. In an exemplary embodiment, longitudinal adhesive-free spacings effectively increase the width of an optical-fiber ribbon formed of reduced-diameter optical fibers so that the optical-fiber ribbon achieves a more conventional optical-fiber ribbon width, thereby facilitating mass-fusion splicing using standard splicing equipment.

FIELD OF THE INVENTION

The present invention relates to optical-fiber ribbons and methods for producing optical-fiber ribbons.

BACKGROUND

Optical fibers provide advantages over conventional communication lines. As compared with traditional wire-based networks, optical-fiber communication networks can transmit significantly more information at significantly higher speeds. The amount of data transmitted over optical-fiber cables is continuously increasing worldwide. This is especially so in data centers because of the expansion of cloud computing, which requires that data be received and transmitted in limited physical space. As such, there is an increasing demand for high-fiber-count and high-fiber-density optical cables. Moreover, there is persistent desire to reduce construction costs of access cable networks, making the reduction of optical-cable diameter and weight central to the use of existing facilities (e.g., underground ducts) to reduce installation costs. Another practical requirement is the ability to mass-fusion splice optical fibers to shorten the time required for connecting cables. This means that there are several—possibly conflicting—demands, such as decreasing optical-cable diameters, increasing optical-fiber density, and improving optical-cable workability. This is a serious and difficult challenge for optical-cable manufacturers.

To achieve easy workability, optical-fiber ribbons can preferentially be mass-fusion spliced to simultaneously make multiple optical-fiber connections. Conventional optical-fiber ribbons have the disadvantage of rigidity, however, because of the application of a resin layer around the optical-fiber assembly to keep the optical fibers in a parallel plane. This rigidity limits the possibility of increasing fiber density in optical-fiber cables.

It is well known to connect two optical fibers end-to-end by fusion splicing with a laser, electric arc, or the like. The splicing usually includes preparing each optical fiber's end portion by stripping the coatings (e.g., the outer secondary coating and inner primary coating) from each optical fiber's outer glass cladding and inner glass core, and precisely cleaving each optical fiber's outer glass cladding and inner glass core to yield a bare glass end to be spliced. Typically, the respective cleaved, bare glass ends are precisely aligned in a single-splice, fusion-splicing machine that joins the two optical fibers. The splice alignment and other accommodations help to minimize any attenuation at the splice and provide a strong connection between the spliced ends.

The single-splicing machine typically includes opposite holding mechanisms for respectively holding the optical fibers so that the cleaved, bare glass ends can be precisely aligned. To facilitate alignment, each holding mechanism (e.g., a single-fiber alignment chuck) can include a platform or tray defining a V-shaped groove for precisely retaining each optical fiber's cleaved, bare end portion. Additionally, each alignment chuck or holding mechanism can further include a portion for precisely securing each optical fiber's coated portion adjacent to the cleaved, bare end portion.

Similarly, it is well known to collectively splice two optical-fiber ribbons end-to-end by mass-fusion splicing. Each optical-fiber ribbon, for example, may include twelve optical fibers that are held together by adhesive material. Preparing each optical-fiber ribbon's end portion typically includes separating the constituent optical fibers' respective end portions and then preparing each optical fiber to yield bare glass end portions. For efficiency, the respective cleaved, bare glass ends are precisely aligned in a mass-fusion splicing machine that joins the respective optical fibers.

The mass-fusion splicing machine (e.g., a mass-fusion splicer) typically employs opposite holding mechanisms (e.g., alignment chucks) for respectively securing the optical fibers so that their cleaved, bare glass ends can be precisely aligned. To facilitate alignment, each alignment chuck or other holding mechanism can include a platform or tray respectively defining a plurality of V-shaped grooves (e.g., 12 grooves or 24 grooves) for precisely retaining each optical fiber's cleaved, bare end portion. Additionally, each alignment chuck or other holding mechanism can further include a part or a portion for precisely securing each optical fiber's coated portion adjacent to the cleaved, bare end portion.

Flexible optical-fiber ribbons yield increased optical-fiber density in optical-fiber cables. Mass splicing such flexible optical-fiber ribbons requires positioning the optical-fiber ribbons in alignment chucks of a mass-fusion splicing machine, but sometimes the adhesive bonds (e.g., elongated beads) may cause interference within the alignment chucks (e.g., the V-shaped grooves in the alignment chuck). For example, some commercially available alignment chucks (e.g., used in mass-fusion splicing machines) cannot readily accommodate flexible optical-fiber ribbons if the pitch of the adhesive-bead pattern is too short (e.g., less than about 100 millimeters), because of adhesive-bead interference in the alignment chucks' V-shaped grooves. Alternatively, if the pitch of the adhesive-bead pattern becomes too long, flexible optical-fiber ribbons can become very flexible and difficult to load into the alignment chucks. A solution requires applying tension to both ends of the optical-fiber ribbon and positioning the edge of the optical fiber at either end of the alignment chuck to achieve proper loading of the optical-fiber ribbon into the alignment chuck.

Moreover, flexible optical-fiber ribbons employing reduced-diameter optical fibers can further increase optical-fiber density in optical-fiber cables. Mass splicing flexible optical-fiber ribbons formed of reduced-diameter optical fibers is complicated, however, and some manufacturers have not commercialized mass-fusion splicing machines specifically designed for optical fibers having diameters of 200 microns or less. The choices for 200-micron mass-fusion splicing machines are limited (and the mass-fusion splicers are expensive, too), and using a conventional mass-fusion splicing machine designed for nominal 250-micron optical fibers to mass splice an optical-fiber ribbon formed of reduced-diameter optical fibers (e.g., including 180-micron and 200-micron optical fibers) introduces alignment problems. Splicing two optical-fiber ribbons that include reduced-diameter optical fibers (e.g., two 200-micron-optical-fiber ribbons)—or splicing two optical-fiber ribbons that respectively include reduced-diameter optical fibers (e.g., 180-micron and 200-micron optical fibers) and nominal 250-micron optical fibers—sometimes requires the use of a pitch-conversion optical-fiber holder to align the respective glass core and claddings (e.g., the respective 125-micron glass optical fibers). In brief, satisfactory alignment of the respective optical-fiber glass cores is difficult to achieve when mass fusion splicing ribbonized, reduced-diameter optical fibers using a conventional mass-fusion splicing machine designed for nominal 250-micron optical fibers.

SUMMARY

It is an exemplary object of the present invention to provide an optical-fiber ribbon having excellent flexibility, strength, and robustness to facilitate rolling or folding of the constituent optical fibers in the ribbon-width direction. It is another exemplary object of the present invention to provide an optical-fiber ribbon that can be readily mass-fusion spliced to make multiple optical-fiber connections.

In one aspect, the present invention embraces an optical-fiber ribbon that includes a plurality of respectively adjacent optical fibers (e.g., twelve or more reduced-diameter optical fibers, such as 180-micron optical fibers or 200-micron optical fibers) extending in a longitudinal direction and arranged in parallel to form an optical-fiber assembly having a width w extending crosswise to a longitudinal length of the optical-fiber assembly. The optical fibers are arranged in a plurality of respectively adjacent optical-fiber units. The optical-fiber ribbon further includes bonding material on the optical-fiber assembly (e.g., deposited on a major surface of the optical-fiber assembly, such as its upper planar surface) adhesively bonding adjacent optical-fiber units and the corresponding adjacent optical fibers in the optical-fiber assembly so that at least one adjacent pair of optical-fiber units is separated by an adhesive-free spacing for a portion of the optical-fiber assembly's longitudinal length. Typically, each adjacent pair of optical-fiber units is separated by an adhesive-free spacing for a respective portion of the optical-fiber assembly's longitudinal length.

An optical-fiber ribbon formed of reduced-diameter optical fibers might be too narrow for equipment used for mass-fusion splicing optical-fiber ribbons formed of conventional 250-micron optical fibers (e.g., the V-shaped grooves in standard alignment chucks are too widely spaced). The longitudinal adhesive-free spacings effectively increase the width of an optical-fiber ribbon formed of reduced-diameter optical fibers so that the optical-fiber ribbon achieves a more conventional optical-fiber ribbon width, which facilitates mass-fusion splicing using standard splicing equipment.

In a related aspect, the present invention embraces a method of making an optical-fiber ribbon. An exemplary method includes (i) arranging a plurality of optical fibers into a longitudinal optical-fiber assembly in which the optical fibers are distributed into a plurality of respectively adjacent optical-fiber units that are spatially separated from one another, the optical-fiber assembly having a width w extending crosswise to a longitudinal length of the optical-fiber assembly; (ii) advancing the longitudinal optical-fiber assembly at linear velocity v while maintaining spatial separation between adjacent optical-fiber units; and (iii) applying bonding material to the optical-fiber assembly to adhesively bond adjacent optical-fiber units and the corresponding adjacent optical fibers in the optical-fiber assembly while maintaining spatial separation between the adjacent optical-fiber units.

Exemplary optical-fiber ribbons have excellent flexibility, strength, and robustness to facilitate rolling or folding of the constituent optical fibers in the ribbon-width direction. In addition, exemplary optical-fiber ribbons can be mass-fusion spliced to make multiple optical-fiber connections, and individual optical fibers can be separated without damaging adjacent optical fibers. Each optical fiber typically includes, from its center to its periphery, a glass core, a glass cladding, and one or more coatings (e.g., a primary coating, a secondary coating, and an optional ink layer). As such, corresponding embodiments of the optical-fiber ribbon herein disclosed are applicable to the related method for making an optical-fiber ribbon, and vice versa.

The foregoing illustrative summary, other objectives and/or advantages of the present disclosure, and the manner in which the same are accomplished are further explained within the following detailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described hereinafter with reference to the accompanying drawings in which embodiments of the present invention are shown and in which like reference numbers indicate the same or similar elements. The drawings are provided as examples, may be schematic, and may not be drawn to scale. The present inventive aspects may be embodied in many different forms and should not be construed as limited to the examples depicted in the drawings.

FIG. 1 is a pictorial view of a section of an exemplary optical-fiber assembly in accordance with a first embodiment of this disclosure.

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a pictorial view of a section of an exemplary optical-fiber assembly in accordance with a second embodiment of this disclosure.

FIG. 4 is a top plan view of an optical-fiber ribbon in accordance with the first embodiment of this disclosure.

FIG. 5 is a side elevation view depicting an exemplary method of making an optical-fiber ribbon in accordance with the first and second embodiments of this disclosure.

FIG. 6 is a top pictorial view depicting a portion of FIG. 5 in accordance with the first embodiment of this disclosure.

DETAILED DESCRIPTION

Various aspects and features are herein described with reference to the accompanying figures. Details are set forth to provide a thorough understanding of the present disclosure. It will be apparent, however, to those having ordinary skill in the art that the disclosed optical-fiber ribbons and methods for producing optical-fiber ribbons may be practiced or performed without some or all of these specific details. As another example, features disclosed as part of one embodiment can be used in another embodiment to yield a further embodiment. Sometimes well-known aspects are not described in detail to avoid unnecessarily obscuring the present disclosure. This detailed description is thus not to be taken in a limiting sense, and it is intended that other embodiments are within the spirit and scope of the present disclosure.

In a first aspect, the present invention embraces an optical-fiber ribbon that includes a plurality n of respectively adjacent optical fibers (e.g., twelve or more reduced-diameter optical fibers, such as 180-micron optical fibers or 200-micron optical fibers) extending in a longitudinal direction and arranged in parallel to form an optical-fiber assembly, which has a width w extending crosswise to a longitudinal length of the optical-fiber assembly. The n optical fibers are arranged in a plurality U of respectively adjacent optical-fiber units. The optical-fiber ribbon further includes bonding material on the optical-fiber assembly (e.g., deposited on a major surface of the optical-fiber assembly, such as its upper planar surface) adhesively bonding adjacent optical-fiber units and the corresponding adjacent optical fibers in the optical-fiber assembly so that at least one adjacent pair of optical-fiber units is separated by an adhesive-free spacing for a portion of the optical-fiber assembly's longitudinal length. Typically, each adjacent pair of optical-fiber units is separated by a longitudinal adhesive-free spacing for a respective portion of the optical-fiber assembly's longitudinal length.

As noted, an optical-fiber ribbon formed of reduced-diameter optical fibers (e.g., 180-micron optical fibers or 200-micron optical fibers) might be too narrow for conventional equipment used for mass-fusion splicing optical-fiber ribbons formed of conventional 250-micron optical fibers (e.g., the V-shaped grooves in standard alignment chucks are too widely spaced for the reduced-diameter optical fibers). According to the present invention, the incorporation of longitudinal adhesive-free spacings in the optical-fiber assembly effectively increases the width of an optical-fiber ribbon formed of reduced-diameter optical fibers so that the optical-fiber ribbon achieves a more conventional optical-fiber ribbon width. This increased width facilitates mass-fusion splicing using a conventional mass-fusion splicing machine (e.g., mass fusion splicers designed for nominal 250-micron optical fibers) to mass splice an optical-fiber ribbon formed of reduced-diameter optical fibers (e.g., nominal 180-micron optical fibers and/or 200-micron optical fibers). For example, splicing two optical-fiber ribbons that include reduced-diameter optical fibers (e.g., two 180-micron or 200-micron optical-fiber ribbons)—or splicing two optical-fiber ribbons that respectively include reduced-diameter optical fibers (e.g., 180-micron optical fibers or 200-micron optical fibers) and nominal 250-micron optical fibers—can be achieved using a conventional mass-fusion splicing machine designed for nominal 250-micron optical fibers without the use of additional equipment (e.g., a pitch-conversion optical-fiber holder).

In a related second aspect, the present invention embraces a method of making an optical-fiber ribbon with adhesive-free spacings (e.g., longitudinal gaps along a portion of the optical-fiber assembly). An exemplary method includes (i) arranging a plurality n of optical fibers into a longitudinal optical-fiber assembly in which the n optical fibers are distributed into a plurality U of respectively adjacent optical-fiber units that are spatially separated from one another, the optical-fiber assembly having a width w extending crosswise to a longitudinal length of the optical-fiber assembly; (ii) advancing the longitudinal optical-fiber assembly at linear velocity v while maintaining spatial separation between adjacent optical-fiber units; and (iii) applying bonding material to the optical-fiber assembly to adhesively bond adjacent optical-fiber units and the corresponding adjacent optical fibers in the optical-fiber assembly while maintaining spatial separation between the adjacent optical-fiber units. In an exemplary process embodiment, the n optical fibers are passed through an alignment die (e.g., an aggregating die), which is configured to provide spatial separation between adjacent optical-fiber units, to provide the plurality U of respectively adjacent optical-fiber units.

The bonding material may be applied to the optical-fiber assembly as a continuous bead or as discontinuous beads, such as disclosed in commonly assigned U.S. Pat. No. 10,782,495, which is hereby incorporated by reference in its entirety. For example, for a portion of the optical-fiber assembly's longitudinal length, the bonding material may be applied as a plurality of successive rectilinear beads arranged lengthwise along the optical-fiber assembly (e.g., the successive beads forming a stepwise pattern across the optical-fiber assembly), so that the adhesive beads are configured to form elongated bonds between adjacent optical fibers in the optical-fiber assembly.

An exemplary method for applying either a continuous bead of bonding material or discontinuous beads of bonding material to an optical-fiber assembly in a way that facilitates faster line speeds during the manufacturing of optical-fiber ribbons is disclosed in commonly assigned U.S. patent application Ser. No. 16/683,827 for an Optical-Fiber Ribbon with Distorted Sinusoidal Adhesive Pattern and Method Therefor, now U.S. Pat. No. 10,884,213, each of which is hereby incorporated by reference in its entirety.

As depicted in FIGS. 1-3, an exemplary optical-fiber assembly 10 includes a plurality of optical fibers 11 arranged side-by-side such that the optical fibers 11 are substantially parallel to one another. Each optical fiber 11 may be closely spaced or contiguous with an adjacent optical fiber 11 within an optical-fiber unit 14 but typically should not cross over one another along the length of the optical-fiber assembly 10. Optical fibers 11 usually include a component glass fiber 12 and one or more surrounding coating layers 13. See FIG. 2. Those having ordinary skill in the art will understand the various kinds of primary coatings, secondary coatings, and ink layers, as well as the structures and thicknesses thereof. This application hereby incorporates by reference commonly owned U.S. Pat. No. 8,265,442 for a Microbend-Resistant Optical Fiber and U.S. Pat. No. 8,600,206 for a Reduced-Diameter Optical Fiber.

FIG. 4 depicts an exemplary optical-fiber ribbon 1, such as formed from an exemplary optical-fiber assembly 10 as depicted in FIGS. 1-2, further including a continuous bead 16 of bonding material (e.g., deposited in a zigzag-like pattern) on the optical-fiber assembly 10 to adhesively bond adjacent optical-fiber units 14 and the corresponding adjacent optical fibers 11. The optical-fiber assembly 10 (and the resulting optical-fiber ribbon 1) have a substantially planar (i.e., flattened) geometry that defines a relatively narrow height, a relatively wide width, and a substantially continuous length (e.g., over 1,000 meters, such as 5,000 meters or more). As illustrated in FIG. 4, each adhesive-free spacing 15 extends along a respective portion of the optical-fiber assembly's longitudinal length but is disrupted as the continuous bead 16 of bonding material (or other adhesive-bead pattern) crosses between respective, adjacent optical-fiber units 14.

The exemplary optical-fiber assembly 10 depicted in FIGS. 1-2 includes three (3) optical-fiber units 14 separated by two (2) adhesive-free spacings 15 (e.g., a 3×4 configuration). That is, each adjacent pair of optical-fiber units is spaced from one another for a portion of the optical-fiber assembly's longitudinal length by a longitudinal adhesive-free spacing 15. Similarly, exemplary optical-fiber assembly 10 depicted in FIG. 3 includes four (4) optical-fiber units 14 separated by three (3) adhesive-free spacings 15 (e.g., a 4×3 configuration). Typically, the n optical fibers are uniformly distributed into the U optical-fiber units whereby each of the U optical-fiber units has the same number u_(n) of optical fibers, such as depicted in FIGS. 1-3. That said, it is within the scope of the invention to unevenly distribute the optical fibers within the optical-fiber units.

As used herein, an optical-fiber assembly 10 as depicted in FIGS. 1-3 inherently defines an upper side (i.e., the top), a lower side (i.e., the bottom), a left edge, and a right edge. The respective upper and lower sides define the major surfaces of the optical-fiber assembly 10 (and the resulting optical-fiber ribbon 1). Those having ordinary skill in the art will appreciate that flipping the optical-fiber assembly 180 degrees over its major transverse axis will reverse the top and bottom, and so the terms can be used interchangeably herein depending on the frame of reference. Similarly, those having ordinary skill in the art will appreciate that yaw rotating the optical-fiber assembly 180 degrees will reverse the right edge and left edge, and so the terms can be used interchangeably herein depending on the frame of reference. Accordingly, as used herein, terms such as “first side” and “second, opposite side” refer to the respective upper and lower sides of the optical-fiber assembly 10 (and the resulting optical-fiber ribbon), or vice versa depending on the frame of reference.

In an exemplary embodiment, each optical fiber has a reduced diameter d of between 150 microns and 230 microns, more typically between about 180 microns and 200 microns. Alternatively, the optical fibers may have a conventional diameter d, such as between about 240 microns and 260 microns. In an exemplary embodiment, the optical-fiber assembly includes between six and 36 optical fibers (including 6 and 36), such as between twelve and 24 optical fibers (including 12 and 24). Typically, each optical fiber in an optical-fiber ribbon has a substantially circular cross section, and all the optical fibers in an optical-fiber ribbon have substantially the same nominal diameter.

As shown in FIGS. 1-3, each adjacent pair of optical-fiber units 14 is separated by an adhesive-free spacing 15 for a respective portion of the optical-fiber assembly's longitudinal length. The respective adhesive-free spacings between adjacent optical-fiber units have a mean width S_(avg). In an exemplary embodiment, the n optical fibers 11 (e.g., twelve reduced-diameter optical fibers) have a mean diameter d_(avg), such as 180 microns or 200 microns, and the respective adhesive-free spacings have a mean width S_(avg) that is at least 50 percent (e.g., at least 75 percent) of the mean diameter d_(avg) of the n optical fibers. In another exemplary embodiment, the n optical fibers (e.g., twelve reduced-diameter optical fibers) have a mean diameter d_(avg), such as 180 microns or 200 microns, and the respective adhesive-free spacings have a mean width S_(avg) that is at least 100 percent (e.g., at least 150 percent) of the mean diameter d_(avg) of the n optical fibers.

By way of comparison, optical fibers may be arranged in parallel and respectively adjacent to each other in a plane (i.e., contiguously positioned within an optical-fiber ribbon). Because no adhesive-free spacings (e.g., longitudinal gaps between adjacent optical-fiber units) are present in a comparative optical-fiber ribbon, the nominal width w of the optical-fiber ribbon reflects the number n and diameter d of the optical fibers (i.e., w≈n×d). The widths w of such comparative optical-fiber ribbons are typically between about 2 millimeters and 10 millimeters (e.g., between 2 millimeters and 6 millimeters, such as about 3 millimeters). In practice, the optical fibers are substantially contiguous to one another, although some small gaps may exist between adjacent optical fibers. The width of the resulting comparative optical-fiber ribbon corresponds to the width w of the comparative optical-fiber assembly.

For example, a comparative optical-fiber ribbon (without adhesive-free spacings or other longitudinal gaps) formed of twelve (12) conventional optical fibers having a mean diameter d₂₅₀ of 250 microns yields a nominal width w of 3000 microns (i.e., 3 millimeters). Similarly, a comparative optical-fiber ribbon (without adhesive-free spacings or other longitudinal gaps) formed of twelve (12) reduced-diameter optical fibers having a mean diameter d of 200 microns yields a nominal width w of 2400 microns (i.e., 2.4 millimeters), and a comparative optical-fiber ribbon (without adhesive-free spacings or other longitudinal gaps) formed of twelve (12) reduced-diameter optical fibers having a mean diameter d of 180 microns yields a nominal width w of 2160 microns (i.e., 2.16 millimeters).

As noted, the incorporation of lengthwise adhesive-free spacings in the optical-fiber assembly in accordance with the present disclosure effectively increases the width of an optical-fiber ribbon formed of reduced-diameter optical fibers so that the optical-fiber ribbon achieves a more conventional optical-fiber ribbon width (e.g., closer to 3000 microns for a 12-optical-fiber ribbon). Increasing the width of an optical-fiber ribbon formed of reduced-diameter optical fibers via adhesive-free spacings facilitates mass-fusion splicing using a conventional mass-fusion splicing machine (e.g., mass fusion splicers designed for nominal 250-micron optical fibers), such as to mass-fusion splice an optical-fiber ribbon formed of reduced-diameter optical fibers (e.g., nominal 180-micron optical fibers and/or 200-micron optical fibers).

In exemplary embodiments, sufficient longitudinal gaps (e.g., adhesive-free spacing) are introduced (e.g., designed) into an optical-fiber ribbon formed of reduced-diameter optical fibers to close the differential with a conventional optical-fiber ribbon (e.g., formed of conventional optical fibers having a mean diameter d₂₅₀ of about 250 microns) by about 50 percent or more (at least 60 percent or 70 percent) such as 80 percent or more (e.g., at least 90 percent or 100 percent). For example, an optical-fiber ribbon formed of twelve (12) reduced-diameter optical fibers having a mean diameter d of 200 microns might include total spacing (e.g., adhesive-free spacings or other longitudinal gaps) that increases the nominal width from 2400 microns (without adhesive-free spacings or other longitudinal gaps) to at least 2700 microns (e.g., between about 2800 microns and 3000 microns).

Table 1 (below) provides the increased nominal width of prophetic optical-fiber ribbons formed of twelve (12) reduced-diameter optical fibers having a mean diameter d_(avg) of 200 microns as compared with a similar optical-fiber ribbon without any adhesive-free spacings (“no spacing”). Here, each exemplary optical-fiber ribbon includes three optical-fiber units (U=3) having four reduced-diameter optical fibers (u_(n)=4) arranged contiguously within each optical-fiber unit, such as the 3×4 configuration depicted in FIGS. 1-2:

TABLE 1 S_(avg) ÷ d_(avg) S_(avg) (μ) d_(avg) (μ) U × u_(n) ribbon width (μ) no spacing 0 200 — 2400  10% 20 200 3 × 4 2440  20% 40 200 3 × 4 2480  30% 60 200 3 × 4 2520  40% 80 200 3 × 4 2560  50% 100 200 3 × 4 2600  60% 120 200 3 × 4 2640  70% 140 200 3 × 4 2680  80% 160 200 3 × 4 2720  90% 180 200 3 × 4 2760 100% 200 200 3 × 4 2800 110% 220 200 3 × 4 2840 120% 240 200 3 × 4 2880 130% 260 200 3 × 4 2920 140% 280 200 3 × 4 2960 150% 300 200 3 × 4 3000 160% 320 200 3 × 4 3040 170% 340 200 3 × 4 3080 180% 360 200 3 × 4 3120 190% 380 200 3 × 4 3160

Table 2 (below) provides the increased nominal width of prophetic optical-fiber ribbons formed of twelve (12) reduced-diameter optical fibers having a mean diameter d_(avg) of 200 microns as compared with a similar optical-fiber ribbon without any adhesive-free spacings (“no spacing”). Here, each exemplary optical-fiber ribbon includes four optical-fiber units (U=4) having three reduced-diameter optical fibers (u_(n)=3) arranged contiguously within each optical-fiber unit, such as the 4×3 configuration depicted in FIG. 3:

TABLE 2 S_(avg) ÷ d_(avg) S_(avg) (μ) d_(avg) (μ) U × u_(n) ribbon width (μ) no spacing 0 200 — 2400  10% 20 200 4 × 3 2460  20% 40 200 4 × 3 2520  30% 60 200 4 × 3 2580  40% 80 200 4 × 3 2640  50% 100 200 4 × 3 2700  60% 120 200 4 × 3 2760  70% 140 200 4 × 3 2820  80% 160 200 4 × 3 2880  90% 180 200 4 × 3 2940 100% 200 200 4 × 3 3000 110% 220 200 4 × 3 3060 120% 240 200 4 × 3 3120 130% 260 200 4 × 3 3180

Comparing Table 1 and Table 2 illustrates that, all things being equal, increasing the number of optical-fiber units (and thus the corresponding number of gaps between adjacent optical-fiber units) increases the nominal width of the optical-fiber ribbon formed of reduced-diameter optical fibers (e.g., having a mean diameter d_(avg) of 200 microns).

Table 3 (below) provides the increased nominal width of prophetic optical-fiber ribbons formed of twelve (12) reduced-diameter optical fibers having a mean diameter d_(avg) of 180 microns as compared with a similar optical-fiber ribbon without any adhesive-free spacings (“no spacing”). Here, each exemplary optical-fiber ribbon includes three optical-fiber units (U=3) having four reduced-diameter optical fibers (u_(n)=4) arranged contiguously within each optical-fiber unit, such as the 3×4 configuration depicted in FIGS. 1-2:

TABLE 3 S_(avg) ÷ d_(avg) S_(avg) (μ) d_(avg) (μ) U × u_(n) ribbon width (μ) no spacing 0 180 — 2160  10% 18 180 3 × 4 2196  20% 36 180 3 × 4 2232  30% 54 180 3 × 4 2268  40% 72 180 3 × 4 2304  50% 90 180 3 × 4 2340  60% 108 180 3 × 4 2376  70% 126 180 3 × 4 2412  80% 144 180 3 × 4 2448  90% 162 180 3 × 4 2484 100% 180 180 3 × 4 2520 110% 198 180 3 × 4 2556 120% 216 180 3 × 4 2592 130% 234 180 3 × 4 2628 140% 252 180 3 × 4 2664 150% 270 180 3 × 4 2700 160% 288 180 3 × 4 2736 170% 306 180 3 × 4 2772 180% 324 180 3 × 4 2808 190% 342 180 3 × 4 2844 200% 360 180 3 × 4 2880 210% 378 180 3 × 4 2916 220% 396 180 3 × 4 2952 230% 414 180 3 × 4 2988 240% 432 180 3 × 4 3024 250% 450 180 3 × 4 3060 260% 468 180 3 × 4 3096 270% 486 180 3 × 4 3132 280% 504 180 3 × 4 3168

Table 4 (below) provides the increased nominal width of prophetic optical-fiber ribbons formed of twelve (12) reduced-diameter optical fibers having a mean diameter d_(avg) of 180 microns as compared with a similar optical-fiber ribbon without any adhesive-free spacings (“no spacing”). Here, each exemplary optical-fiber ribbon includes four optical-fiber units (U=4) having three reduced-diameter optical fibers (u_(n)=3) arranged contiguously within each optical-fiber unit, such as the 4×3 configuration depicted in FIG. 3:

TABLE 4 S_(avg) ÷ d_(avg) S_(avg) (μ) d_(avg) (μ) U × u_(n) ribbon width (μ) no spacing 0 180 — 2160  10% 18 180 4 × 3 2214  20% 36 180 4 × 3 2268  30% 54 180 4 × 3 2322  40% 72 180 4 × 3 2376  50% 90 180 4 × 3 2430  60% 108 180 4 × 3 2484  70% 126 180 4 × 3 2538  80% 144 180 4 × 3 2592  90% 162 180 4 × 3 2646 100% 180 180 4 × 3 2700 110% 198 180 4 × 3 2754 120% 216 180 4 × 3 2808 130% 234 180 4 × 3 2862 140% 252 180 4 × 3 2916 150% 270 180 4 × 3 2970 160% 288 180 4 × 3 3024 170% 306 180 4 × 3 3078 180% 324 180 4 × 3 3132 190% 342 180 4 × 3 3186

Comparing Table 3 and Table 4 illustrates that, all things being equal, increasing the number of optical-fiber units (and thus the corresponding number of gaps between adjacent optical-fiber units) increases the nominal width of the optical-fiber ribbon formed of reduced-diameter optical fibers (e.g., having a mean diameter d_(avg) of 180 microns).

In a related aspect, the present invention embraces targeting mean gap width S_(avg) of the respective longitudinal adhesive-free spacings for an optical-fiber ribbon as a function of the number and nominal width (e.g., 250 microns) of a conventional optical fiber. In an exemplary embodiment, the optical-fiber ribbon includes a plurality n of respectively adjacent optical fibers (e.g., twelve or more reduced-diameter optical fibers, such as 180-micron optical fibers or 200-micron optical fibers) extending in a longitudinal direction and arranged in parallel to form an optical-fiber assembly, which has a width w extending crosswise to a longitudinal length of the optical-fiber assembly. The n optical fibers have the same nominal diameter d and are uniformly distributed into a plurality U of respectively adjacent optical-fiber units (e.g., each optical-fiber unit has the same number of optical fibers u_(n)). The optical-fiber ribbon further includes bonding material on the optical-fiber assembly (e.g., deposited on a major surface of the optical-fiber assembly, such as its upper planar surface) adhesively bonding adjacent optical-fiber units and the corresponding adjacent optical fibers in the optical-fiber assembly so that each adjacent pair of optical-fiber units is separated by a longitudinal adhesive-free spacing for a respective portion of the optical-fiber assembly's longitudinal length. The respective longitudinal adhesive-free spacings within the optical-fiber assembly (and the resulting optical-fiber ribbon) have a mean gap width S_(avg), wherein:

-   -   S_(avg) (f·n·(d₂₅₀·d))÷(U−1), where f is a factor representing         the amount of spacing within the optical-fiber assembly and d₂₅₀         is 250 microns, the nominal width of a conventional optical         fiber.

As noted, in exemplary embodiments, sufficient longitudinal gaps (e.g., adhesive-free spacing) are incorporated into an optical-fiber ribbon formed of reduced-diameter optical fibers (e.g., optical fibers having nominal diameter d of between about 180 microns and 200 microns) to close the differential with a conventional optical-fiber ribbon (e.g., formed of conventional optical fibers having a mean diameter d₂₅₀ of about 250 microns) by about 50 percent or more (e.g., f≥0.5, such as f≥0.7), or even 75 percent or more (e.g., f≥0.75, such as f≥0.95). For example, an optical-fiber ribbon formed of twelve (12) reduced-diameter optical fibers having a mean diameter d of 200 microns might have an f factor of at least 0.5 to provide total spacing (e.g., adhesive-free spacings or other longitudinal gaps) to increase the optical-fiber ribbon's nominal width from 2400 microns (without adhesive-free spacings or other longitudinal gaps) to at least 2700 microns (e.g., between about 2800 microns and 3000 microns). Similarly, an optical-fiber ribbon formed of twelve (12) reduced-diameter optical fibers having a mean diameter d of 180 microns might have (i) an f factor of at least 0.5 to provide total spacing (e.g., adhesive-free spacings or other longitudinal gaps) to increase the optical-fiber ribbon's nominal width from 2160 microns (without adhesive-free spacings or other longitudinal gaps) to at least 2580 microns (e.g., between about 2600 microns and 2800 microns) or (ii) an f factor of at least 0.7 to provide total spacing (e.g., adhesive-free spacings or other longitudinal gaps) to increase its nominal width from 2160 microns (without adhesive-free spacings or other longitudinal gaps) to at least about 2750 microns (e.g., between about 2800 microns and 3000 microns).

As shown in the process schematic depicted in FIGS. 5-6 (processing from right to left), a plurality n of optical fibers 11 (e.g., 12 or 24 reduced-diameter optical fibers) are arranged into a longitudinal optical-fiber assembly 10 in which the n optical fibers 11 are distributed into a plurality U of respectively adjacent optical-fiber units 14 that are spatially separated from one another. As such, the optical-fiber assembly 10 has a width w extending crosswise to a longitudinal length of the optical-fiber assembly 10.

As shown in FIGS. 5-6, the plurality n of loose optical fibers 11 are passed through a die 24 that is configured to align the optical fibers in parallel and provide spatial separation between adjacent optical-fiber units 14. This, in turn, provides the plurality U of respectively adjacent optical-fiber units, each of which includes adjacent and substantially parallel optical fibers 11. As it exits the die 24, the optical-fiber assembly 10 is a loose arrangement of substantially parallel optical fibers 11 with no bonding between the optical fibers and having interstices or grooves between adjacent optical fibers within each optical-fiber unit 14. When employing an aggregating die 24 to align the optical fibers 11 and separate the optical-fiber units 14, the entry speed of the loose optical fibers 11 is the same as the exit speed of the longitudinal optical-fiber assembly 10.

During processing, the longitudinal optical-fiber assembly 10 advances at linear velocity v, typically at a linear speed greater than 150 meters per minute (e.g., greater than 200 meters per minute, such as greater than 300 meters per minute), while maintaining spatial separation between adjacent optical-fiber units 14. In some exemplary embodiments, the longitudinal optical-fiber assembly 10 advances at linear velocity v between 400 and 700 meters per minute (e.g., between about 500 and 600 meters per minute). As the optical-fiber assembly 10 passes near (e.g., beneath) a dispenser unit 25 (or similar dispensing device), bonding material (e.g., a curable adhesive) is applied to the optical-fiber assembly 10 to adhesively bond adjacent optical-fiber units 14 and the corresponding adjacent optical fibers 11 in the optical-fiber assembly while maintaining spatial separation between the adjacent optical-fiber units 14. For example, the bonding material may be dispensed as a continuous adhesive bead 16 (or a plurality of discontinuous beads) via a dispensing nozzle 26 to a major surface of the optical-fiber assembly 10 (e.g., its upper planar surface). Thereafter, the optical-fiber assembly with an adhesive bead is passed through a curing station 28 for curing the bonding material (e.g., a curable adhesive, such as curable ultraviolet (UV) resins). See FIG. 5.

In an exemplary process embodiment, the dispenser 25 and/or the dispensing nozzle 26 move crosswise substantially corresponding to the width w of the longitudinal optical-fiber assembly 10. In this way, the bonding material is applied as an adhesive bead 16 across at least one major surface of the optical-fiber assembly (e.g., in a pattern on the upper planar surface substantially across the width of the optical-fiber assembly). As will be understood by those having ordinary skill in the art, providing an adhesive bead “substantially across the width” of the optical-fiber assembly bonds adjacent optical fibers to yield an optical-fiber ribbon (e.g., the adhesive deposition patterns extend to the outermost opposite optical fibers in the optical-fiber assembly).

In a related process embodiment, the dispenser 25 and/or the dispensing nozzle 26 move crosswise substantially corresponding to the lateral distance (w−2d) between the two outermost optical fibers. As will be understood by those having ordinary skill in the art, this lateral distance (w−2d) is the separation between the outermost grooves in the optical-fiber assembly. As used herein, terms like “substantially corresponding to the width” and “substantially corresponding to the lateral distance” refer to the movement of a dispensing nozzle and/or the corresponding adhesive deposition patterns, which typically extend to the outermost opposite optical fibers in the optical-fiber assembly (e.g., opposite edge portions of the optical-fiber assembly).

Typically, the adhesive bead bonding adjacent optical fibers in the optical-fiber assembly forms a regular pattern (continuous or discontinuous) across the width of the optical-fiber assembly, such as a zigzag-like pattern, a sawtooth-like pattern, or a sinusoidal-like pattern having a peak-to-valley amplitude substantially between (i) the lateral distance between the two outermost optical fibers (w−2d) and (ii) the width w of the optical-fiber assembly. (Some excess bonding material may be present outside one or both outermost optical fibers in the optical-fiber ribbon.) In some exemplary process embodiments, the dispensing nozzle may pause when positioned above grooves in the optical-fiber assembly to deposit bonding material as longitudinal, rectilinear adhesive beads within the respective grooves (e.g., grooves between contiguous optical fibers).

By way of background and illustration, the respective cross-sectional areas of exemplary adhesive beads can be approximated by 125-micron equilateral-triangle sides for 250-micron optical fibers (e.g., about 0.0068 mm²) and by 100-micron equilateral-triangle sides for 200-micron optical fibers (e.g., about 0.0043 mm²). With a +/−20 percent estimation of bead dimensions, the respective ranges for cross-sectional areas of the beads can be approximated by 100-micron to 150-micron equilateral-triangle sides for the 250-micron optical fibers (e.g., between about 0.0043 mm² and 0.0097 mm²) and by 80-micron to 120-micron equilateral-triangle sides for the 200-micron optical fibers (e.g., between about 0.0028 mm² and 0.0062 mm²).

In exemplary embodiments, the dispenser 25 and/or the dispensing nozzle 26 (or other dispensing device) oscillate in a direction transverse to the longitudinal direction (i.e., in the width direction) of the optical-fiber assembly, and the optical-fiber assembly moves in the longitudinal direction, such as via a reel 29. The tip of the dispenser 25 (e.g., the dispensing nozzle 26) may oscillate (e.g., vibrate) in a transverse direction at a high frequency, such as between about 100 Hz and 200 Hz. In an exemplary process embodiment, the dispensing nozzle 26 may deliver liquid bonding material in fine droplets to the advancing optical-fiber assembly 10. Because of surface tension, the liquid bonding material—if provided in sufficient droplets at a sufficient frequency—will flow together to form adhesive beads (e.g., elongated beads).

In other exemplary embodiments, the dispenser 25 and/or the dispensing nozzle 26 (or other dispensing device) revolve in a plane parallel to a planar optical-fiber assembly. This has been observed to promote faster line speeds during the manufacturing of a continuously or intermittently bonded optical-fiber ribbon, such as an optical-fiber ribbon with a distorted sinusoidal pattern of bonding material. In this regard, an exemplary dispensing nozzle 26 is made of a capillary tube at the center of a metallic sleeve that is revolving in a substantially circular orbit via a servomotor (e.g., using belt-pulley system). Such a configuration reduces undesirable vibrations, which can be caused by the linear motion of a conventional reciprocating crank shaft as typically used with reciprocating nozzles, and avoids overlapping and/or uneven distribution of bonding material, which can occur using a conventional reciprocating crank shaft. Indeed, it has been observed that the use of a revolving nozzle helps to achieve linear velocities v between 400 and 700 meters per minute, which is about 4-5 times greater than is possible with a conventional reciprocating-crank-shaft system.

It is within the scope of the present disclosure to have either one substantially continuous adhesive bead or a series of discontinuous beads that secure (e.g., affix) the optical fibers within the optical-fiber ribbon. In an exemplary embodiment, the adhesive bead(s) are arranged on only one side of the optical-fiber assembly (i.e., a first side). For example, the bead(s) are arranged only on one major surface of the optical-fiber assembly, typically its upper surface (i.e., when the optical fibers are arranged in a ribbon-like manner rather than rolled up). As noted, the optical-fiber assembly can be viewed as a ribbon-like assembly defining an upper surface, a lower surface, and two side edges. The upper and lower surfaces (i.e., the respective major surfaces) are not completely flat, because they are formed of a substantially parallel arrangement of optical fibers. As such, the upper and lower surfaces have parallel longitudinal grooves between adjacent optical fibers. Those having ordinary skill in the art will understand the optical fibers may not be perfectly parallel but rather substantially parallel in practice.

As discussed, in exemplary optical-fiber ribbons according to the present invention, bonding material adhesively bonds adjacent optical-fiber units and the corresponding adjacent optical fibers in an optical-fiber assembly. Two such optical-fiber ribbons may be aligned and joined using a mass-fusion splicing machine. For example, corresponding 12-fiber optical-fiber ribbons may be positioned in respective 12-fiber alignment chucks and, after heat stripping, cleaning, and cleaving, the two optical-fiber ribbons may be spliced at once (e.g., the corresponding optical fibers can be simultaneously butt-spliced end-to-end in the mass-fusion splicing machine).

The optical-fiber ribbon according to the present invention may be used to form optical-fiber-cable units and optical-fiber cables. An exemplary optical-fiber-cable unit has 24 ribbons of twelve optical fibers each. Such an optical-fiber-cable unit packs 288 optical fibers into a high optical-fiber density. Accordingly, in another inventive aspect, the present invention embraces an optical-fiber-cable unit including one or more optical-fiber ribbons (also according to the present invention) surrounded by a polymeric sheath. The present invention further embraces an optical-fiber cable including one or more of the optical-fiber ribbons or optical-fiber-cable units according to the present invention.

To supplement the present disclosure, this application incorporates entirely by reference the following commonly assigned patents, patent application publications, and patent applications: U.S. Pat. No. 7,623,747 for a Single Mode Optical Fiber; U.S. Pat. No. 7,889,960 for a Bend-Insensitive Single-Mode Optical Fiber; U.S. Pat. No. 8,145,025 for a Single-Mode Optical Fiber Having Reduced Bending Losses; U.S. Pat. No. 8,265,442 for a Microbend-Resistant Optical Fiber; U.S. Pat. No. 8,600,206 for a Reduced-Diameter Optical Fiber; U.S. Pat. No. 10,185,105 for a Flexible Optical-Fiber Ribbon; U.S. Pat. No. 10,782,495 for a Flexible Optical-Fiber Ribbon; International Application No. PCT/EP2017/067454 (filed Jul. 11, 2017, and published as International Publication No. WO 2019/011417 A1 and as U.S. Patent Application Publication No. US2020/0271879 A1); International Application No. PCT/EP2018/050898 (filed Jan. 15, 2018, and published as International Publication No. WO 2019/137627 A1); International Application No. PCT/EP2018/050899 (filed Jan. 15, 2018, and published as International Publication No. WO 2019/137628 A1); U.S. patent application Ser. No. 16/856,268 (filed Apr. 23, 2020, and published as U.S. Patent Application Publication No. US2020/0386961 A1); and U.S. patent application Ser. No. 17/130,589 for an Optical-Fiber Ribbon with Adhesive-Free Gaps (concurrently filed Dec. 22, 2020).

Other variations of the disclosed embodiments can be understood and effected by those of ordinary skill in the art in practicing the present invention by studying the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Unless otherwise specified, numerical ranges are intended to include the endpoints.

It is within the scope of this disclosure for one or more of the terms “substantially,” “about,” “approximately,” and/or the like, to qualify each adjective and adverb of the foregoing disclosure, to provide a broad disclosure. As an example, it is believed those of ordinary skill in the art will readily understand that, in different implementations of the features of this disclosure, reasonably different engineering tolerances, precision, and/or accuracy may be applicable and suitable for obtaining the desired result. Accordingly, it is believed those of ordinary skill will readily understand usage herein of the terms such as “substantially,” “about,” “approximately,” and the like.

The use of the term “and/or” includes any and all combinations of one or more of the associated listed items. The figures are schematic representations and so are not necessarily drawn to scale. Unless otherwise noted, specific terms have been used in a generic and descriptive sense and not for purposes of limitation.

While various aspects, features, and embodiments have been disclosed herein, other aspects, features, and embodiments will be apparent to those having ordinary skill in the art. The various disclosed aspects, features, and embodiments are for purposes of illustration and are not intended to be limiting. It is intended that the scope of the present invention includes at least the following claims and their equivalents: 

The invention claimed is:
 1. An optical-fiber ribbon, comprising: (i) a plurality n of respectively adjacent optical fibers extending in a longitudinal direction and arranged in parallel to form an optical-fiber assembly having a width w extending crosswise to a longitudinal length of the optical-fiber assembly, wherein the n optical fibers have the same nominal diameter d and wherein the n optical fibers are uniformly distributed into a plurality U of respectively adjacent optical-fiber units whereby each of the U optical-fiber units has the same number u_(n) of optical fibers; and (ii) bonding material on the optical-fiber assembly adhesively bonding adjacent optical-fiber units and the corresponding adjacent optical fibers in the optical-fiber assembly, wherein each adjacent pair of optical-fiber units is separated by a longitudinal adhesive-free spacing for a respective portion of the optical-fiber assembly's longitudinal length, the respective longitudinal adhesive-free spacings having a mean gap width S_(avg), wherein: S_(avg)≥(0.5·n·(d₂₅₀−d))÷(U−1), where d₂₅₀ is 250 microns, the nominal width of a conventional optical fiber.
 2. The optical-fiber ribbon according to claim 1, wherein the respective longitudinal adhesive-free spacings have a mean gap width S_(avg), wherein: S_(avg)≥(0.7·n·(d₂₅₀−d))÷(U−1), where d₂₅₀ is 250 microns, the nominal width of a conventional optical fiber.
 3. The optical-fiber ribbon according to claim 1, wherein adjacent optical fibers within each optical-fiber unit are respectively contiguous to one another.
 4. The optical-fiber ribbon according to claim 1, wherein, for a portion of the optical-fiber assembly's longitudinal length, the bonding material comprises a continuous bead of bonding material.
 5. The optical-fiber ribbon according to claim 1, wherein, for a portion of the optical-fiber assembly's longitudinal length, the bonding material comprises a plurality of successive elongated rectilinear beads arranged lengthwise along the optical-fiber assembly, wherein the beads are configured to form elongated bonds between adjacent optical fibers in the optical-fiber assembly.
 6. The optical-fiber ribbon according to claim 1, wherein the respective longitudinal adhesive-free spacings have a mean gap width S_(avg), wherein: S_(avg)≥(0.75·n·(d₂₅₀−d))÷(U−1), where d₂₅₀ is 250 microns, the nominal width of a conventional optical fiber.
 7. The optical-fiber ribbon according to claim 1, wherein the respective longitudinal adhesive-free spacings have a mean gap width S_(avg), wherein: S_(avg)≥(0.95·n·(d₂₅₀−d))÷(U−1), where d₂₅₀ is 250 microns, the nominal width of a conventional optical fiber.
 8. The optical-fiber ribbon according to claim 1, wherein each of the n optical fibers has a nominal diameter d of between 180 microns and 200 microns.
 9. The optical-fiber ribbon according to claim 1, wherein the n optical fibers are uniformly distributed into two adjacent optical-fiber units whereby U=2.
 10. The optical-fiber ribbon according to claim 1, wherein the n optical fibers are uniformly distributed into three respectively adjacent optical-fiber units whereby U=3.
 11. The optical-fiber ribbon according to claim 1, wherein the n optical fibers are uniformly distributed into four respectively adjacent optical-fiber units whereby U=4.
 12. The optical-fiber ribbon according to claim 1, wherein the optical-fiber assembly includes between six and 36 optical fibers whereby 6≥n≥36.
 13. The optical-fiber ribbon according to claim 1, wherein the optical-fiber assembly includes between 12 and 24 optical fibers whereby 12≥n≥24.
 14. An optical-fiber ribbon, comprising: (i) a plurality n of respectively adjacent optical fibers extending in a longitudinal direction and arranged in parallel to form an optical-fiber assembly having a width w extending crosswise to a longitudinal length of the optical-fiber assembly, wherein the n optical fibers have the same nominal diameter d of between 180 microns and 200 microns, wherein the n optical fibers are uniformly distributed into a plurality U of respectively adjacent optical-fiber units whereby each of the U optical-fiber units has the same number u_(n) of optical fibers, and wherein adjacent optical fibers within each optical-fiber unit are respectively substantially contiguous to one another; and (ii) bonding material on the optical-fiber assembly adhesively bonding adjacent optical-fiber units and the corresponding adjacent optical fibers in the optical-fiber assembly, wherein each adjacent pair of optical-fiber units is separated by a longitudinal adhesive-free spacing for a respective portion of the optical-fiber assembly's longitudinal length, the respective longitudinal adhesive-free spacings having a mean gap width S_(avg), wherein: S_(avg)≥(0.5·n·(d₂₅₀−d))÷(U−1), where d₂₅₀ is 250 microns, the nominal width of a conventional optical fiber.
 15. The optical-fiber ribbon according to claim 14, wherein the respective longitudinal adhesive-free spacings have a mean gap width S_(avg), wherein: S_(avg)≥(0.7·n·(d₂₅₀−d))÷(U−1), where d₂₅₀ is 250 microns, the nominal width of a conventional optical fiber.
 16. The optical-fiber ribbon according to claim 14, wherein the respective longitudinal adhesive-free spacings have a mean gap width S_(avg), wherein: S_(avg)≥(0.95·n·(d₂₅₀−d))÷(U−1), where d₂₅₀ is 250 microns, the nominal width of a conventional optical fiber.
 17. The optical-fiber ribbon according to claim 14, wherein the n optical fibers are uniformly distributed into two adjacent optical-fiber units whereby U=2.
 18. The optical-fiber ribbon according to claim 14, wherein the n optical fibers are uniformly distributed into three respectively adjacent optical-fiber units whereby U=3.
 19. The optical-fiber ribbon according to claim 14, wherein the n optical fibers are uniformly distributed into four respectively adjacent optical-fiber units whereby U=4.
 20. The optical-fiber ribbon according to claim 14, wherein the optical-fiber assembly includes between six and 36 optical fibers whereby 6≥n≥36.
 21. The optical-fiber ribbon according to claim 14, wherein the optical-fiber assembly includes between 12 and 24 optical fibers whereby 12≥n≥24. 